scope:

Hard coating always aims at adapting the behaviour of a component or tool to the requirements of a specific application. This mostly comprises several steps. In many cases, it is only by way of hard coating that certain applications are rendered possible. Whether or not a coating shows the expected effect can, at long last, only be checked under on-site conditions (field test). In some fields, application-oriented tests have therefore been developed (e.g. specific drilling and cutting tests), which provide information on the actual on-site behaviour of a hardcoated component or tool. As a matter of principle, these tests are best suited for quality assurance provided that they can be performed at reasonable time and cost expenditure. However, as these tests are highly specific (they have often been developed to match the needs of one product only), they cannot be dealt with in this guideline. Descriptions of such tests are mostly found in in-house quality management systems. The notes on inspection planning as per Section 3 of this guideline, however, also apply to the performance of this kind of tests.

It is often impossible to carry out field tests or specific tests for quality-assurance purposes because of their high financial or technical demands, or for lack of such tests. In this case, a model test (DIN 50 323-2) shall be performed. It may refer to

• functional system properties, i.e. to the behaviour of the complete coated component or tool under specified stresses, e.g. tribological properties,
• functional properties of the composite of hard coating and basis material, e.g. composite hardness or scratch resistance,
• structural properties of the hard coating proper, e.g. hardness and modulus of elasticity or coating thickness.

Part of the tests may be carried out on the coated workpiece itself. In many cases, however, it is only possible to test reference samples.

This part of the guideline presents methods from these fields of model testing of hard coatings, which are widely accepted among job coaters. The question always to be asked is whether a selected procedure actually covers the properties relevant to the application, and allows reproducible testing.

The testing of optical, decorative, electrical, and other functional coatings which do not serve to protect from wearing or to reduce friction, is expressly excluded from the scope of this guideline. Likewise, the varied test procedures important to R&D are not dealt with since most of these are highly complex, and they are only used in exceptional cases for routine quality assurance. However, they are of great importance for damage assessment and the identification of sources of errors.